Phagocytosis-stimulating mediators in insects

The ability of insect blood cells to ingest all kinds of synthetic particles and also a wide range of microorganisms in a very short time after injection has up to now been regarded as a phagocytic function without any humoral mediators. In a phagocytosis model with latex beads and nonhagocytosable cells of Bacillus thuringiensis subtoxicus, we are able to demonstrate the existence of lymphokine-like factors, which intervene in cellular defence reactions of insect. The following results were obtained: 1. Immediately after injection of latex beads, normally non-phagocytosable cells of Bacillus thuringiensis subtoxicus are phagocytosed. 2. Cell-free haemolymph of larvae of Galleria mellonella previously injected with latex beads, stimulates in new larvae phagocytosis of Bacillus thuringiensis subtoxicus after transfusion. 3. The fractionation of homogenates of latex-treated larvae on Sephadex G 50 shows two fractions which stimulate phagocytosis. We suppose that the appearance of these phagocytosis-stimulating factors is the result of a successful recognition of foreign material.